Saturday, April 21, 2018

#PAW2018 Medical Moment ~ Acute Intermittent Porphyria


#PAW2018 

This is one of the hereditary hepatic porphyrias. Its inheritance is autosomal dominant. The deficient enzyme is porphobilinogen deaminase (PBGD), also known as hydroxymethylbilane synthase (HMB synthase). This enzyme was formerly known as uroporphyrinogen I-synthase, and this term is still used by some clinical laboratories. A deficiency of PBGD is not sufficient by itself to produce AIP, and other activating factors must also be present. These include hormones, drugs and dietary changes. Sometimes, activating factors cannot be identified.
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  Symptoms
Most people who inherit the gene for AIP never develop symptoms. However, experts recommend that all relatives of someone with AIP obtain testing, to determine who has the genetic trait and who does not. Those who test positive for the trait should be educated as to measures that will help avoid attacks. Prevention is essential to good management.

AIP manifests after puberty, especially in women (due to hormonal influences). Symptoms usually come as discrete attacks that develop over two or more days. Abdominal pain, which is associated with nausea, can be severe and occurs in most cases.

Other symptoms may include:
·       nausea
·       vomiting
·       constipation
·       pain in the back, arms and legs
·       muscle weakness (due to effects on nerves supplying the muscles)
·       urinary retention
·       palpitation (due to a rapid heart rate and often accompanied by increased blood pressure)
·       confusion, hallucinations and seizures
Sometimes the level of salt (sodium and chloride) in the blood decreases markedly and contributes to some of these symptoms. The skin is not affected.

Diagnosis

Because this disease is rare and can mimic a host of other more common conditions, its presence is often not suspected. On the other hand, the diagnosis of AIP and other types of porphyria is sometimes made incorrectly in patients who do not have porphyria at all, particularly if laboratory tests are improperly done or misinterpreted. The finding of increased levels of delta-aminolevulinic acid (ALA) and porphobilinogen (PBG) in urine establishes that one of the acute porphyrias is present. If PBGD is deficient in normal red blood cells, the diagnosis of AIP is established. However, measuring PBGD in red blood cells should not be relied upon by itself to exclude AIP in a sick patient, because the enzyme is not deficient in red blood cells of all AIP patients.
If it is known that someone in a family has AIP, and their enzyme value is low in red blood cells, other family members who have inherited a deficiency of PBGD can be identified by measuring the enzyme in their red blood cells. Latent cases so identified can avoid agents known to cause attacks. However, in some AIP families, PBGD is normal in red blood cells and is deficient only in the liver and other tissues. Falsely low values sometimes occur due to problems with collecting and transporting the sample.
DNA is the material in cells that encodes all the genetic information of an individual. Many different mutations have been identified in the portion of DNA that comprises the gene for PBGD. However, within a given family, everyone has the same mutation. When that mutation is known for one member, screening of the relatives is straightforward and can be done on DNA from saliva (spit) or a swab of the inside of the cheek. This is now the gold standard of diagnosis and is available through specialty labs. Details are available from the APF or investigators of the national Porphyria Consortium http://rarediseasesnetwork.epi.usf.edu/porphyrias/index.htm.

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